Remove all shebangs from Python modules and checker

As discussed, Python modules which aren't intended to be invoked
as scripts should not include a shebang line.

Update CONTRIBUTING.md and the checker script.
This script now includes a list SKIP_FILES for files that
should not be checked for boilerplate template.
The tests will now fail if a Python module has a shebang line.
Scripts which should have a shebang line and exists in the directory
`hack` can be ignored by adding them to the SKIP_FILES list.

Author: oz123

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 Thanks for taking the time to join our community and start contributing!
 
-Any changes to utilites in this repo should be send as a PR to this repo.
+Any changes to utilities in this repo should be send as a PR to this repo.
 After the PR is merged, developers should create another PR in the main repo to update the submodule.
 See [this document](https://github.com/kubernetes-client/python/blob/master/devel/submodules.md) for more guidelines.
 
@@ -11,3 +11,19 @@ provides detailed instructions on how to get your ideas and bug fixes seen and a
 
 Please remember to sign the [CNCF CLA](https://github.com/kubernetes/community/blob/master/CLA.md) and
 read and observe the [Code of Conduct](https://github.com/cncf/foundation/blob/master/code-of-conduct.md).
+
+## Adding new Python modules or Python scripts
+If you add a new Python module please make sure it includes the correct header
+as found in:
+```
+hack/boilerplate/boilerplate.py.txt
+```
+
+This module should not include a shebang line.
+
+If you add a new Python helper script intended for developers usage, it should
+go into the directory `hack` and include a shebang line `#!/usr/bin/env python`
+at the top in addition to rest of the boilerplate text as in all other modules.
+
+In addition this script's name should be added to the list   
+`SKIP_FILES`  at the top of hack/boilerplate/boilerplate.py.

config/__init__.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 # Copyright 2016 The Kubernetes Authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

config/config_exception.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 # Copyright 2016 The Kubernetes Authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

config/dateutil.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 # Copyright 2017 The Kubernetes Authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

config/dateutil_test.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 # Copyright 2016 The Kubernetes Authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

config/exec_provider.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 # Copyright 2018 The Kubernetes Authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

config/exec_provider_test.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 # Copyright 2018 The Kubernetes Authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

config/incluster_config.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 # Copyright 2016 The Kubernetes Authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

config/incluster_config_test.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 # Copyright 2016 The Kubernetes Authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");

config/kube_config.py

@@ -1,5 +1,3 @@
-#!/usr/bin/env python
-
 # Copyright 2018 The Kubernetes Authors.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");